AT AN investor briefing in 2015, Masayoshi Son, chief executive of SoftBank, flashed up a picture of a goose. The company is like the bird of legend that produces golden eggs, he explained. In his quest to encourage more laying, Mr Son has taken SoftBank well beyond its telecoms business. The firm also manages the world’s largest tech-investment fund, the $100bn Vision Fund, which has a slew of wealthy backers, including Saudi Arabia’s Public Investment Fund and Apple.

Using both the firm and the fund, Mr Son has acquired stakes in tech companies at a frenetic pace, by one count opening his chequebook once every four days on average in 2017. Such shopping sprees do not come cheap. SoftBank is one of Japan’s most highly leveraged companies, with debt exceeding ¥15trn ($139bn), not least because of its purchase in 2013 of a controlling stake in Sprint, an American mobilenetwork operator.

News reports this week suggest SoftBank is now hatching a plan to raise ¥2trn by...